Flash heating apparatus for diamond synthesis from liquid carbon



' July@ 1961 1. BRAYMAN 3,328,841 FLASH HEATING APPARATUS vFOR DIAMOND lv SYNTHESIS FROM LIQUID CARBON Filed-April 17,l 1963 v l f 2 Sheets-Sheet 1' TEMPERATURE ('K) INVENTOR ancoa BRAYMAN BYM *007;2-1

FLASH HEATING APPARATUS FOR DIAMOND SYNTHESIS FROM LIQUID CARBON FiledApril 17,. 1963 2'- Sheers-sneez a mvE'N'ron .mcoe annum A' BY l UnitedStates Patent O York Filed Apr. 17, 1963, Ser. No. 273,785 8 Claims.(Cl. 18-16.5)

This invention relates generally -to the synthesis of diamond from softcarbon. More particularly, this invention relates to means for directlyconverting sort carbon to diamond.

De Carli and Jamieson in an -article (1) entitled Formation of Diamondby Explosive Shock and published in Science (volume 133, No. 3467, pages1821-1822, June 1961) have described the application to a graphitesample of a shock wave generated by a conventional explosive charge andof an estimated value of 300 kilobars. While the shock wave was observedto produce diamonds, the yield of diamonds was so minute as to benegligible, and the diamonds themselves were of such small size (l0microns or less in diameter) as to have no practical utility.

More recently, F. P. Bundy in an article (2) entitled Direct Conversionof Graphite to Diamond in Static Pressure Apparatus and published inScience (volume 13'7, No. 3535, pages 1057-1058, Sept. 28, 1962) and inanother -article (3) entitled New Phase Transitions in Extended Regionsof Pressure and Temperature and publicized at the A.I.M.E. Symposium(Dallas, Tex., Feb. 24- 28, 1963) has disclosed the conversion todiamond of part of a small bar of graphite by the application to thatbar of a static pressure of about 130 kilobars and by the flash heatingofthe bar to a temperature of about 3500 K.

Thus, it is now known that soft carbon can vbe converted into diamonddirectly, i.e., without the intervention of a molten metallic agent fordissolving the carbon.

An object of this invention is to diamondize soft carbon directly byapparatus having advantages over those now known to the prior art..

These and other objects are realized according to the invention byheating a charge including soft carbon to a temperature and under apressure by which at least some of the carbon is rendered in the stableliquid state. The liquidized carbon is then cooled under pressureconditions which produce resolidication of at least part of the carbonin the form of diamond, and which also, permit recovery ofthediamondized car-bon.

The charge itself may consist wholly of soft carbon (i.e. graphite oramorphous carbon) or may consist of soft carbon admixed with othersubstances. Ordinarily, the charge forms one component of apressure-receiving container of which another component is a casing ofpressure transmissible material disposed around the charge. To initiatethe method, the container is placed in a press and the press is thenactuated to exert on the exterior of the container a static pressurewhich is communicated through the pressure transmissive material of thecasing to the central charge. Conveniently, the press may be of a typewhich uses tapered pressure-exerting elements or anvils to effectpressure-multiplication. Thus, the press may be, say, of the well knownbelt type or it may be, say, a cubic or tetrahedral press of the typedisclosed in U.S. Patent 2,968,837 issued Jan. 24, 1961 in the name ofZeitlin et al. or, as an alternative example, it may lbe acylindric-prismatic press of the type disclosed in U.S. Patent 3,080,609issued on Mar. 12, 1963 in the name of Gerard et al. Where, however, thestatic pressure employed in the method is relatively low (e.g. on theorder of kilobars or less), the press which is used need not necessarilybe a pressure-multiplying press.

The charge is heated according to the present method Fice by a ashheating produced by a transient discharge of electric current throughthe container. An advantage of so ash heating the charge is that theperiod of heating is so short that the container casing and the presssurfaces in cont-act with that casing do not become appreciably heatedby conduction or radiation of heat from the charge.

As later described more fully, according to one way of practicing themethod the diamondizing of the carbon and the subsequent cooling thereofis promoted by the application to the heated charge of a transientpressure which contributes to the total pressure on the carbon, andwhich also drives the liquied carbon into forcible contact with thecooler medium provided by the casing to thereby resolidify or freeze thecarbon almost instantaneously. Preferably, but not necessarily, thetransient pressure is generated by a transient discharge of electriccurrent through the container to produce therein a high energy rate arcdischarge through a non-metallic medium or, alternatively, thevaporizing of a metallic medium in the torm of, say, an exploding wireMoreover, pref. erably but not necessarily, the transient pressure is awavepropagated pressure manifested by a pressure wave which desirably isbut need not be a shock wave, i.e., a wave which travels through amedium under given pressure and temperature conditions lat a speedfaster than sound.

For a better understanding of the invention, reference is made to thefollowing description of representative methods and means embodying theinvention and to the accompanying drawings wherein:

FIG. l is a phase diagram of carbon; and

FIG. 2 is a schematic view in `cross-section of one form of pressingmeans and pressure-receiving container for the invention.

The diagram of FIG. l is a phase diagram of carbon under variouspressure (P) and temperature (T) conditions, pressure being plottedvertically in kilobars and temperature being plotted horizontally indegrees Kelvin. The FIG. 1 diagram is a modified version of a similarphase diagram shown in the aforementioned article (2).

In FIG. 1, the circle 20 at about 130 kb. and 4100 K. is thediamond-graphite-liquid triple point for carbon. The point 20 isconnected by a downwardly extending graphite melting line 21 to agraphite-liquid-vapor triple point 22 at about 0.12 kb. and about 4100K. A line 23 extending rightward from point 22 separates a liquid carbonphase region 24 above that line from a vapor carbon phase region 25below the line. Note that the graphite melting line 21 extends fromtriple point 22 'down to zero pressure. This means that at pressuresbelow about 0.12 kb., carbon will sublime from the solid state to thevapor state as the temperature is raised to that required to producecarbon vapor.

Above the triple point 20, the liquid phase region 24 for carbon is tothe right-hand side of a diamond melting line 26. The boundary formed bythe lines 21 and 26 is referred to herein as the carbon meltingboundary. For all P-T conditions to the left of the carbon meltingboundary, carbon is stably in a solid state and can exist as a liquidonly in an unusual sense such as by being dissolved in a molten metallicsolvent or by pseudomelting. To the right of the carbon meltingboundary, carbon is stably in a liquid state.

The area to the left of the carbon melting boundary is divided into P-Tregions of interest as follows.

Extending downwardly and leftwardly from triple point 20 is -a line 30known as the Simon-Berman line. Above line 30 and between that line andline 26 is a P-T region in which diamond is stable. Below the Simon-Berman line 30 and between such line and the graphite melting line 21 isa P-T region in which graphite is stable.

The diamond-stable region above line 30 is further subdivided into anupper region 31 and a lower region 32 by a line 35 extending from triplepoint 20 and known as the graphite melting line extension. The upperregion 31 is an exclusive diamond region in that within that regiondiamond is stable but graphite cannot persist even in a metastable statefor any significant time. Within the lower region 32, diamond is stableand graphite is metastable.

The graphite-stable region below Simon-Berman line 30 is shown in FIG. 1as being sub-divided by (a) a line 37 from triple point 20 known as thediamond melting line extension, (b) a line 33 referred to herein as thefast graphitizing line. The two last named lines will later beldiscussed in more detail.

The positions on the FIG. l diagram of the lines 21 and 30 have beenwell established by a large amount of experimental work. The position,on the other hand, of the line 35 is based on a lesser `amount ofexperimental work and on a determination of that position byextrapolation from such Work. Because the position shown in FIG. 1 ofthe line 35 has so been determined by resort to extrapolation, thatposition is not necessarily representative of the exact actual bounds ofthe described P-T regions 31 and 32 on the opposite sides of line 35.The presence, however, of these regions has been well confirmed byexperimental evidence.

In FIG. l, the line 38 is based on experimental results reported in theaforementioned articles (2) and (3). The said line represents theapproximate demarcation between a region to the left thereof where noobservable graphitizing of diamond occurred within a period on the orderof milliseconds and a region to the right thereof where completegraphitizing of diamonds took place within that period. Thus,considering the graphite-stable region bounded by lines 30 and 21, whilein theory it is the line 37 which separates an exclusive graphite regionon the right thereof from a stable-graphite metastable-diamond region onthe left thereof, as a matter of practice the bound between thoseleftward and rightward regions can better be considered as representedby the line 38. Such exclusive graphite region rightward of line 38 isdesignated in FIG. 1 by the reference numeral 42, and it is a region inwhich graphite is stable but in which diamond cannot persist for anysignificant length of time in even the metastable state.

Within the region under the Simon-Berman line 30 and to the left of thefast diamondizing line 38, diamond is metastable but has a tendency tographitize at a rate dependent on the pressure and temperature to whichthe diamond material is subjected. Qualitatively speaking, that regioncan be sub-divided into separate regions 44 and 43 which arerespectively disposed leftward and right- Ward of the slowgraphitization line 39. The latter line has been plotted on FIG. 1mostly from experimental data given by F. P. Bundy in an article (4)entitled Diamond- Graphite Equilibrium Line From Growth andGraphitization of Diamond and published in the Journal of ChemicalPhysics (vol. 35, No. 2, pages 383-391, August 1961).

Within the region 44 bounded by lines 30 and 39, diamond undergoes noobservable graphitizing within a relatively long time period (eg. tenminutes). As the P-T point moves leftwardly from line 39, thegraphitizing rate progressively drops off until at atmospheric pressureand room temperature (330 K.) the rate is essentially zero. It is thisessentially zero graphitizing rate which accounts for the indefinitelylong persistence of diamonds under ordinary conditions.

In the region 43, diamond graphitizes at an appreciable rate whichincreases in the direction generally indicated by the arrow 45. That is,the graphitizing rate increases with a decrease in pressure or with anincrease of temperature or with the -occurrence of both. As indicatedpreviously, in the vicinity of line 39 the graphitizing rate isrelatively slow in that it requires a period on the order of minutes ortens of minutes to produce observable graphitization. It is only when`the P-T condition arrives at or near to the fast diamondizing line 38that the graphitizing rate becomes so fast that observablegraphitization takes place within a period on the order of milliseconds.

From the description heretofore given, it is evident that to effectconversion of soft carbon to diamond without intervention of a moltenmetallic solvent, it is necessary to subject the soft carbon toconditions of pressure and temperature corresponding to a point in theFIG. 1 diagram at which diamondizing takes place. Various exemplary waysof how this is done according to the present invention will now begiven.

Referring to FIG. l, the point Y represents atmospheric pressure (onebar) and lroom temerature (about 300 Kelvin). Assuming that apressure-receiving container with a charge therein comprised of graphite(or another 'form of soft carbon) has been placed in a suitable press,the first step of the method is to actuate the press to apply pressureto the container and the contained charge. According to Example I (alfirst way of practicing the method), that pressing step develops on thecharge a static pressure of about 10l kb. The application of such staticpressure is represented in FIG. 1 by an upward movement along the linesegment X from the point Y to the point A.

While under such static pressure, the charge is flash heated to atemperature at which the carbon in the charge is brought to a P-T-condition for which carbon is stably a liquid. Such flash heatingoccurs within a period on the order of from ones to tens ofmilliseconds, the heating step being represented in FIG. 1 by right-Ward horizontal movement along the static pressure line P1 from thepoint A to the point B in region 24. Note that, in the course of suchmovement, the P-T condition of the carbon progresses from the region tothe left of line 21 in which carbon is stably solid to the region at theright of line 21 in which carbon is stably of a phase other than solid.Note, moreover, that, because the carbon is under suitable staticpressure, the attained P-T point B is above the vapor region 25,wherefore the carbon does not sublime in the course of the crossing ofline 21 `by the P-T condition of the carbon. In general, the staticpressure applied to the charge during the flash heating should be enoughto maintain the end point B above line 23 which separates the liquidregion 24 from the vapor region 25. Otherwise, the value of static pres-Sure -used is discretionary.

The charge is heated so rapidly by the flash heating that the casingmaterial around the charge has no opportunity to become appreciablyheated by conduction or radiation of heat from the charge. Therefore, atthe end of the ash heating step, the bulk of the casing material is muchcooler than the charge material.

As described, the flash heating produces a liquication of the carbon inthe charge. Thereafter, but before the car-bon has had an opportunity toundergo any appreciable cooling, the charge is subjected to ahigh-magnitude transient pressure which is preferably a wave-propagatedpressure generated by a shock wave. A first effect of the shock wave onthe charge is to greatly increase for an instant the total pressure onthe charge. That increase in total pressure is represented in FIG. 1 -byupward movement from point B along the line M to the point C. As shown,point C has a pressure value well above the pressure characterizing thegraphite-diamond-liquid triple point 20.

A second effect of the shock wave is to produce rapid cooling of theliquid carbon yby -fragmentizing the charge so as to drive the carbon inthe form of molten droplets into the adjacent cooler casing material.When the molten carbon droplets are so forced into contact with the muchcooler medium provided by the casing, the `droplets freeze almostinstantaneously by virtue of loss of heat to the medium. Such freezingtakes place so rapidly that aaaasiti it occurs while the carbon is stillbeing subjected to the transient pressure developed by the shock wave.Therefore, the cooling step is suitably represented in FIG. 1 byleftward movement of the P-T condition of the carbon from Ipoint C alongline N to the point D.

In the course of such leftward movement, the P-T condition of the carbonleaves the liquid region 24 and passes into region 31 within which thecarbon resolidifes. As stated, the region 31 is an exclusive diamondregion in that, while the diamond form of carbon is stable therein, thegraphite form of carbon cannot persist therein even metastably.Accordingly, the carbon resolidifies in diamondized form.

Further leftward movement in FIG. 1 of the P-T condition of the coolingcarbon brings that condition into the region 32 in which diamond isstable and graphite is metastable. In this latter region, nographitizing occurs of the obtained diamond material, and, accordingly,the diamondized material is preserved for later recovery.

As the carbon cools, the transient pressure from the shock wavedissipates to thereby produce a fall in the total pressure on thecarbon. That drop in total pressure is represented in FIG. 1 partly bythe downward inclination from right to left of the line N and partly bythe line L extending downward from point D. The subsidence of -both thecooling effect and the transient pressure effect of the shock waverenders the carbon in a P-T condition represented in FIG. 1 by the pointE. Thereafter, the carbon cools in a manner represented by leftwardmovement in FIG. 1 from point E along line P1 back to the point A.Because the carbon was initially heated by flash heating, the coolingalong line P1 takes place rapidly. Therefore, even though point E is inregion 43 within which diamond graphitizes, t-he time period whichelapses before the P-T condition of the carbon crosses line 39 is soshort that there is no appreciable graphitizing in that period of thediamondized carbon. Once, of course, that the 'P-T` condition of thecarbon crosses line 39 to enter the region 44 and thereafter a-ttain thepoint A, the graphitizing rate of the diamondized carbon is negligible.

The method is completed by removing the static pressure exerted on thecontainer (the corresponding movement in CE-IG. 1 being from point Adown along line segment X to point Y). Thereafter, the container isopened to recover therefrom the yield of diamond Inaterial.

In FIG. 1, the .lines M, N and L Aare to be taken more as qualitativelyillustrating the pressure and temperature variation caused by the shockwave than as accurately indicating in a quantatative sense the transientP-T variation. The reason why those lines should so be considered isthat there is no reliable means for measuring accurately theinstantaneous pressure and temperature values caused by the shock wave.

The method may also be practiced in a way which is referred to herein asExample II, and which does not require the generation of a sho-ck wave.According to Example II, the container and the charge therein are firstsubjected by carbide pressure-mul-tiply-ing anvils to a static pressurewhich is above that characterizing the graphite-diamon-d-liquid triplepoint. The static pressure application 4is represented in FIG. 1 -byupward movement from point Y along line segments X and X to point A.Preferably, the static pressure is on the order of about 150 -kilobarssince such Va pressure value can be exerted by carbide anvils withoutbreakage thereof over a number of compressing cycles.

Next, while the full static pressure is maintained, the charge is flashheated as before to liquify the carbon by bringing the P-T conditionthereof into the region 24 within which carbon is stably a liquid. Thisheating step is represented in FIG. 1 by rightward movement from point Aalong the horizontal static-pressure line P2 to the point B. As in thecase of point B, the pressure value 6 characterizing point B is`sufficient lto preclude Vaporizing of the carbon at -the highesttemperature attained thereby.

After the car-bon in the charge has been liquied by the 'flash heating,the charge is simply allowed to cool while full static pressure ismaintained thereon. The cooling step is, therefore, -represented in FIG.1 by a movement from point B' back along the static pressure line P2 tothe point A. During this leftward movement, the P-T condition of thecarbon leaves the liquid region 24 by passing as before into the region31 within which carbon resolidies in the form of diamonds. Thus,diamondizing of the carbon takes pl-ace. Further cooling brings the P-Tcondition into region 32 `and back to point A' therein. The entireregion 32 is, however, a P-T region in which diamond does notgraphitize. Hence, in the course of cooling to the condition representedby point A', there is no loss of the diamond material obtained by theinitial resolidioation of the carbon in region 31.

The `final step of the method accord-ing to Example II is, of course, toremove the static pressure from the container (the correspondingmovement in FIG. 1 being from point A down along line segments X and Xback to point Y). `Because in such movement, the P-T condition of thecarbon passes directly from the non-graphitizing region 32 to the region44 within which the graphitizing rate is negligible, no loss of diamondmaterial is occasioned by the static pressure removal. As before, whenthe point Y is reached, the container is opened and the yield of diamondmaterial is recovered.

In the method accord-ing to Example I-I, the maintenance of full staticpressure during the cooling of the carbon serves alone to cause -the P-Tcondition of the carbon to follow a path in FIG. 1 which is welldisplaced from those P-T regions within which diamond .graphitizes Inother words, Example II contrasts with Example -I in that, in the methodas practiced according to Example II, 4graphitization is avoidedirrespective of the rate at which the carbon cools. Therefore, inExample II, the rate need only be sufficiently rapid to avoidoverheating of the anvils. It is desirable to use as slow a cooling rate.as will satisfy the last name-d requirement in order thereby toincrease the particle size of the diamonds produced upon resolidicationof the carbon. The cooling rate may, of course, be slowed down byincreasing the time period over which the charge is heated whether by atransient discharge of current or by, say, a short application of steadystate current.

Reference is now made to FIG. 2 which illustra-tes apparatus forcarrying out the method according to Example I. In FIG. 2, a cubicpressure-receiving container 50 is shown as being contacted bypressure-multiplying anvils 51-54 of cemented carbide. The yanvils 51-54form four of a set of six identical anvils hav-ing respective frontfaces of which each contacts a respective one of the six outside facesof container 50i. Those six anvils are components of a cubicpressure-multiplying press such as, say, a cubic press of the sortdisclosed .in U.S. Patent 2,968,837 issued on Jan. 24, 19611 in the nameof Zeitlin et al. Each .anvil front face is square and is 1.74" on aside, whereas the cubic container 50 is 3" on a side. Because each anvilface is smaller than the face contacted thereby of the container, thevarious anvils are separated from each other by inter-anvil gaps 59.

To provide for more effective -compression of container 50, the edgesand vertices thereof may he reinforced by exible sheet coverings in themanner taught in co-pending `application S.N. 240,049 filed Nov. 26,1962 in the r name of Brayman et al. and owned Iby the assignee of thisis a 11/2" long, cylindrical mandrel 65 of silver chloride. As `taughtin co-pending application S.N. 240,691 filed Nov. Z8, 1962 in the nameof Zeitlin et al. and owned by the assignee of this application, nowPatent No. 3,175,068, the mandrel has formed on its cylindrical surfacea helical groove 66 which progresses axially from one end of the mandrelto the other. Within this groove is seated a continuous graphite wire 67of 0.052 diameter. The graphite wire 67 may be fabricated by depositinga graphite paste in groove 66 and then allowing the paste to harden. Asis evident, the wire 67 provides for the method the charge of softcarbon.

The wire 67 is contacted at opposite ends of mandrel 65 by a pair of 1Adiameter copper conductor rods 71 and 72 at right angles to the mandrelaxis and extending outwardly from wire 67 through, respectively, theupper block 61 and the lower block 62. The outer end of rod '71 is flushwith the upper outside face of block 61 and is in electrical contactwith the front face of anvil 51. Analogously, the outer end of rod 72 isflush with the lower outside face of block 62 and is in electricalcontact with the fro-nt face of anvil 52.

The mandrel 65 has therein a central axial bore containing a 0.020diameter (approximately) Nichrome exploding wire 75 -contacted atopposite ends by a pair of metal tabs 66, 67 lying flat against theopposite ends of the mandrel. The. tabs 66 and 67 are, in turn,respectively contacted by the inward ends of a pair of 1A" diameter,copper electrode plugs 78 and 79 extending axially in the mentioned borein opposite directions away from the mandrel. The plugs are held inposition within Vthe bore by two pyrophyllite sleeves `80 and 81 ofwhich each surrounds a respective one of the plugs. As shown, the outerend of plug 78 makes electrical contact through a metal tab -82 with theleft hand horizontal anvil 53, whereas the outer end of plug 79 makescontact through a metal ta-b 83 with the front face of the right-handhorizontal -anvil 54.

The Vertical anvils 51 and 52 are connected in a flash heating circuitof which other components are a switch S1 and a schematically4represented capacitor storage bank 85 chargeable through the terminals86 and 87. The horizontal anvils are likewise connected in an electricalcircuit, namely an exploding wire circuit of which `other components area switch S2 and a schematically represented capacitor storage bank 90chargeable through the terminals 91 and 92. P-referably, the twocircuits are electrically isolated from each other to the extent thateach circuit offers a very high impedance to current flowing in theother. If desired, an auxiliary spark gap (not shown) may beincorporated for current control purposes in each circuit `between thecapacitor bank thereof and one of the anvils connected in such circuit.In each circuit, the capacitor storage bank has an energy storagecapacity of about 60,000 joules.

The switches S1 and S2 of the two circuits are each of the trigatrontype or of the `thyratron type. Each of the switches is closed by aseparate trigger signal from a common electronic timer T which causes-aclosure of S2 `a predetermined time interval after the closure of S1.Devices suitable for use as timer T are well known in the electronicart. For a teaching on capacitor banks providing a large energy storageand on circuits suitable for the large transient discharge currentsproduced by such banks, reference is made to the text Exploding Wiresedited by W. G. Chase and H. K. Moore (Plenum Press, New York, 1959).

The FIG. 2 apparat-us operates as follows to carry out the methodaccording to Example I. First, the anvils which surround container 50are simultaneously actuated to exert pressure on the container. Underthis anvil pressure, the pyrohyllite around the edges of the containertends to flow into the inter-anvil gaps 59 to there form autogenousgaskets in a manner wel-l-known to the art. The same anvil pressuredevelops in the central part of the container a hydrostatic pressurewhich is communicated as a pressure of about l0 kb. to the graphite wireor charge 67.

Once the Igraphite charge is under static pressure, the timer T isactuated to send to switch S1 a trigger signal Serving to close theswitch. Upon the closure of the switch S1, the previously changedcapacitor bank produces a transient discharge of current at a highenergy rate through the helical graphite wire 67 by way of the anvils51, 52 and the rods 71 and 72. The discharge current through graphitewire 67 produces the flash heating and liqui-fication of lthe graphitewhich has been previously described.

Because the graphite wire 67 is flash heated, the temperature of thewire reaches its peak (represented by point B in FIG. 1) within `aperiod on the order of ones or tens of milliseconds from the closure ofswitch S1. After a time delay approximating this period (i.e., beforethe graphite wire has had an opportunity to cool appreciably and, also,before the pyrophyllite in the blocks 71 and 72 has had time to heatappreciably), the timer T sends out a second trigger signal, this timeto the switch S2 to produce closure of :the last-named switch. Whenswitch S2 so closes, the previously charged capacitor bank produces atransient discharge of current at a high energy rate through theexploding wire 75 by way of the anvils 53, 541- and by way of theelectrode plugs 78, 79 (and associated metal tabs). In response to thistransient discharge of current therethrough, the wire 75 vaporizes andexplodes to generate the previously described shock wave.

The shock wave serves (as earlier described) both to develop a transientpressure on the now liquied carbon and to fragmentize the mandrel 65land the liquid charge of carbon. The shock wave furthermore drivesdroplets of liquid carbon from the fragmentized charge into forciblecontact with the cooler pyrophyllite surounding the charge to therebyproduce the described almost instantaneous freezing in the form ofdiamond material of the previously liquid carbon.

Upon sufficient cooling of the carbon, the anvils are retrac-ted fromthe container to receive the static pressure thereon and to permitremoval of the container from the press. The anvil retraction operationcompletes the carrying out of the method insofar as the FIG. 2 apparatusis concerned.

While the foregoing has been a description of the use of the FIG. 2apparatus in practicing the method according to Example l, it will beappreciated that the same apparatus may be employed in connection withthe practice of the method according to Example II. When, however, themethod is practiced according to the latter example, the exploding wire75 and the circuit and circuit cornponents associated therewith areomitted, the timer T may also be omitted (i.e., switch S1 can in thisinstance be a conventional switch), and the anvils are actuated to exerton the graphite charge 67 a pressure of about 150 kilobars in contrastto the pressure of about 10 kb. exerted on the charge during thepractice of the method according to Example I.

`The above described methods and means being exemplary only, it will beunderstood that additions thereto, omissions therefrom and modificationsthereof can be made without departing from the invention, and that theinvention comprehends embodiments differing in form and/or detail fromthose specifically disclosed. For example, in lieu of using rodconductor 72 (FIG. 2), the graphite wire 67 may be extended leftward toconnect with the copper plug '78, and the flash heating circuit may beconnected between the anvils 51 and 53 to thereby use the latter anvilas a common anvil for both the flash heating circuit and the explodingwire circuit. In this manner one of the terminals on the outside ofcontainer 50 may be eliminated while, at the same time, the currents inthe two circuits are maintained independent in the sense that neithercircuit acts as a by-pass for current in the other circuit.

Accordingly, the invention is not to be considered as limited save as isconsonant with the recitals of the following claims.

I claim:

1. A pressure receiving container comprising, a charge in saidcontainer, a casing of pressure-transmissive material disposed aroundsaid charge and providing the exterior of said container, means in saidcontainer .and responsive to electric current to exert a transientpressure on said charge, a plurality of at least three current terminalsdisposed at separate locations on the exterior of said container, meansdefining between a rst pair of said terminals a path through saidcontainer for heating current for said charge, and means definingbetween a second pair of said terminals a path through said containerfor current for said pressure-exerting means, said second pair ofterminals excluding at least one of the terminals in said rst pairthereof.

2. A container as in claim 1 in which said first pair of terminals iscomprised of two terminals disposed on first opposite sides of saidcontainer, andv said second pair of terminals is comprised of anothertwo terminals disposed on second opposite sides of said container.

3. A container as in claim 2 in which said first opposite sides are atright angles to said second opposite sides.

4. Apparatus comprising, a pressure-receiving container, a charge insaid container, a casing of pressure-transmissive material disposedaround said charge and providing the exterior of said casing, aplurality of pressure-multiplying anvils disposed around said containerto be separated by inter-anvil gaps and to operably compress saidcontainer along center lines of actions lying in dilierent planes, meansincluding a first pair of terminals each on the outside of saidcontainer and electrically coupled with a respective one of a iirst pairof said anvils to provide a first path through said container forelectric current, and means including a second pair of terminals each onthe outside of said container and electrically coupled with a respectiveone of a second pair of said anvils to provide a second path throughsaid container for electric current, said second pair of terminals andsaid second pair of anvils excluding, respectively, at least oneterminal in said rst pair thereof and at least one anvil in said secondpair thereof.

5. Apparatus comprising, a plurality of pressure multiplying anvilsdisposed in different planes around a central space to compress anobject therein, a first electric circuit connected to a rst pair of saidanvils to pass electric curv rent therethrough and through said objectwhen the latter is in said space vand is contacted by such pair ofanvils, and a second electric circuit connected to a second pair of saidanvils to pass electric current therethrough and through said objectwhen such object is in said space and is contacted by said last-namedanvils, said second pair of anvils excluding at least one of the anvilsin said first pair thereof.

6. Apparatus comprising, a pressure-receiving container having a chargetherein, a first circuit coupled with said container to passtherethrough a first transient discharge of electric current, a secondcircuit coupled with said container to pass therethrough `a secondtransient discharge of electric current, and electronic timer meanscoupled to both circuits to control the relative timing of said twodischarges so as to initiate said second discharge a predetermined timeinterval after the initiation of said iirst discharge.

7. Apparatus comprising, a pressure receiving container having a chargetherein, iirst and second current sources, a iirst circuit for flow ofcurrent from said tirst source through said container, and a secondcircuit for iiow of current from said second source through saidcontainer, each of said circuits offering a high impedance to flowtherein of current produced in said container by the current source inthe other circuit.

8. Apparatus as in claim 7 in which said rst circuit includes a firstpair of pressure multiplying anvils disposed around said container tocompress it and a first pair of terminals disposed on the outside ofsaid container to each be electrically coupled with a respective one ofsaid first anvils, and in which said second circuit includes a secondpair of pressure multiplying anvils disposed around said container atdifferent positions than said rst anvils to compress said container anda second pair of terminals disposed on the outside of said container toeach be electrically coupled with a respective arc of said secondanvils.

References Cited

6. APPARATUS COMPRISING, A PRESSURE-RECEIVING CONTAINER HAVING A CHARGETHEREIN, A FRIST CIRCUIT COUPLED WITH SAID CONTAINER TO PASSTHERETHROUGH A FIRST TRANSIENT DISCHARGE OF ELECTRIC CURRENT, A SECONDCIRCUIT COUPLED WITH SAID CONTAINER TO PASS THERETHROUGH A SECONDTRANSIENT DISCHARGE OF ELECTRIC CURRENT, AND ELECTRONIC TIMER MEANSCOUPLED TO BOTH CIRCUITS TO CONTROL THE RELATIVE TIMING OF SAID TWODISCHARGES SO AS TO INITIATE SAID SECOND DISCHARGE A PREDE-